The present invention relates to a fan guard for an air blowing unit which does not make noise or a short-circuit while the fan is in operation (blowing air), and to an air-conditioning device provided with the fan guard.
One example of the air blowing unit is the outdoor unit of an air-conditioning system. As shown in FIGS. 20 and 21, an outdoor unit (20) of an air-conditioning system is composed of a heat exchanger (21) and a propeller fan (22) which are stored in a box-shaped casing. On the front side of the casing, an air outlet (20a) is formed by a bell mouth (23), which is a fan guide. A grille-structured fan guard (24) for protecting the fan is arranged to cover the air outlet (20a) of the casing.
Rotating the propeller fan (22) causes air to be taken into the casing through the opening for air intake (20b) on the rear side. The air passes through the heat exchanger (21), the propeller fan (22), the bell mouth (23), the air outlet (20a), and the fan guard (24) in this order so as to be blown toward the front of the outdoor unit (20) as indicated with the arrows.
The fan guard (24) has a grille structure where a plurality of protecting ribs (25, 25 . . . ) and a plurality of supporting ribs (26, 26 . . . ) form a fan-shaped lattice. The protecting ribs (25) are extended in the form of rings around the rotation axis of the propeller fan (22) and are made from a steel wire which is circular in cross section in consideration of the outward appearance. On the other hand, the supporting ribs (26) are extended in the radial direction at predetermined intervals orthogonal to the rotation axis (O-Oxe2x80x2) of the propeller fan (22), and are made from a steel wire which is circular in cross section. The supporting ribs (26) are welded to the protecting ribs (25) so as to support them.
This structure of the outdoor unit (20) can protect the propeller fan (22) inside the outdoor unit (20), and also makes the fan (22) harder to be seen from outside, thereby enhancing the exterior of the entire casing and also offering a well-balanced structure in terms of design.
However, the above-described prior art fan guard (24) made from a steel wire requires the welding of the supporting ribs (26) to the protecting ribs (25), which increases the cost.
In addition, when a current caused by the propeller fan (22) passes into the fan guard (24), it cannot smoothly follow the surfaces of the ribs (25, 26) because the surfaces are circular in cross section. As a result, the current is split by the surfaces so as to develop vortexes, which leads to a pressure loss and makes noise.
It would be possible to reduce the pressure loss by forming the ribs (25, 26) flat with respective predetermined widths. At the same time, it would be possible to lower the cost by integrally making the ribs (25, 26) from a synthetic resin.
However, in that case, the current from the propeller fan (22) flowing into the fan guard (24) includes a speed component having a predetermined magnitude in the direction of rotation of the propeller fan (22). This makes the direction of the air flowing from the propeller fan (22) disagree with the angle at which the flat surfaces of the ribs (25, 26) are set so that the current comes into collision with the flat surfaces, thereby developing vortexes. This leads to a pressure loss and makes noise.
The velocity of flow of air generated by the propeller fan (22) differs among different positions in the direction of the radius of the fan (22). As known from the measured data shown in FIG. 13, the current from the outer portions of the blades (22a) of the propeller fan (22) a little closer to the hub (22b) than the tips (27) of the blades (22a) has a higher velocity than the current from the tips (27). The velocity distribution in the direction of the radius of the fan (22) indicates that the velocity of the current decreases from the outer portions of the blades (22a) both towards the hub (22b) side and towards the tips (27) side.
Inside the outer diameter of the hub (22b), a difference in pressure causes a reverse current which goes from the downstream side of the propeller fan (22) to the hub (22b) side. The reverse current interferes with the current flowing in the intended direction, thereby causing an issue of noise.
When the air blowing unit is applied to the outdoor unit of an air-conditioning system as described above, a short-circuit phenomenon occurs. That is, the air blown by the propeller fan (22) after passing through the heat exchanger (21) spreads outward in the direction of the radius of the fan (22) to be drawn towards the rear side, and again goes into the heat exchanger (21). This short-circuit phenomenon, which deteriorates the air conditioning performance, must be avoided as effectively as possible.
However, the current from the propeller fan (22) generally has a speed component in the centrifugal direction, and tends to spread outward in the direction of the radius of the fan (22). As a result, the air flown out through the fan guard (24) adheres to the front-side wall of the casing due to Coanda effect, and travels towards the heat exchanger (21), which may cause a short-circuit. This tendency is more conspicuous in a case where an oblique fan is used instead of the propeller fan.
Each invention of the present application has been contrived with the aim of solving the above-mentioned problems. In order to achieve the object, the inventions are provided with the following effective problem-solving means.
(1) First Invention
The first invention is provided with a frame (4a) arranged around the perimeter of an air outlet (2a) of a fan (6), and with a plurality of board-shaped ribs (41, 41 . . . ) extending radially from the vicinity of the center of the frame (4a) outward in the direction of the radius of the fan (6).
The board-shaped ribs (41) are outward curved in the direction of rotation of the fan (6), and also inclined in the direction of air flowing from the fan (6).
In other words, the first invention comprises a frame (4a) arranged around the perimeter of the air outlet (2a) of the fan (6), and a plurality of board-shaped ribs (41, 41 . . . ) extending radially from the vicinity of the center of the frame (4a) corresponding to the rotation axis (O-Oxe2x80x2) of the fan (6) outward in the direction of the radius of the fan (6). The plurality of board-shaped ribs (41, 41 . . . ) are extended in the direction of rotation of the fan (6) and also inclined in the direction of air blowing from the fan (6).
As stated before, there is a case where the air blowing unit is applied to the outer unit of an air-conditioning system. In this case, the occurrence of a short-circuit must be prevented as much as possible because it decreases the air-conditioning performance. The air taken in through the opening for air intake on the back side of the casing passes through a heat exchanger and then is blown off through the air outlet (2a) on the front side of the fan (6). It is necessary to avoid a phenomenon in which the blown air is again taken in through the opening for air intake and supplied to the heat exchanger. However, the current generated by the fan (6) arranged upstream of the fan guard (4) tends to flow outward in the direction of the radius of the fan (6). Consequently, if nothing is done, it is likely that the current from the fan guard (4) adheres to the surface of the front wall of the casing due to Coanda effect and travels towards the heat exchanger on the rear side, thereby causing a short circuit.
Therefore, in the first invention, the plurality of board-shaped ribs (41) are curved in the direction of rotation of the fan (6). As a result, the board-shaped ribs (41) makes a force (Fr) inward in the direction of the radius of the fan (6) apply on the current outward in the direction of the radius of the fan (6). Consequently, the current from the fan guard (4) is prevented from flowing outward in the direction of the radius of the fan (6), which reduces the occurrence of a short circuit as much as possible.
As stated above, the current generated by the fan (6) and flowing into the fan guard (4) becomes spinning currents having a speed component in the direction of rotation of the fan (6). As a result, if the direction of the current generated by the fan (6) does not agree with the angle at which the board-shaped ribs (41) are installed, the current is split and noise occurs.
Therefore, in the first invention, the board-shaped ribs (41) are inclined in the direction of air flowing from the fan (6). As a result, the direction of the current from the fan (6) agrees with the angle at which the board-shaped ribs (41) are installed, which can reduce the splitting of the current as much as possible, thereby further lowering the noise.
Since the ribs (41) of the first invention are shaped like boards, the current generated by the fan (6) smoothly follows the surfaces of the board-shaped ribs (41). As a result, splitting of current occurs less, which eliminates the pressure loss and lowers the noise.
(2) Second Invention
The second invention is provided with a frame (4a) arranged around the perimeter of an air outlet (2a) of a fan (6), and further with a plurality of board-shaped ribs (41, 41 . . . ) extending radially from the vicinity of the center of the frame (4a) outward in the direction of the radius of the fan (6). The second invention is further provided with a plurality of nearly cylindrical ribs (42, 42 . . . ) which are integrated with the plurality of board-shaped ribs (41, 41 . . . ) and arranged concentrically around the rotation axis (O-Oxe2x80x2) of the fan (6) at predetermined intervals in the direction of the radius of the fan (6).
The board-shaped ribs (41) are curved outward in the direction of rotation of the fan (6), and also inclined in the direction of air flowing from the fan (6).
In other words, the second invention comprises a frame (4a) arranged around the perimeter of the air outlet (2a) of the fan (6), a plurality of board-shaped ribs (41, 41 . . . ) extending radially from the vicinity of the center of the frame (4a) corresponding to the rotation axis (O-Oxe2x80x2) of the fan (6) outward in the direction of the radius of the fan (6), and a plurality of nearly cylindrical ribs (42, 42 . . . ) which are integrated with the plurality of board-shaped ribs (41, 41 . . . ) and arranged concentrically around the rotation axis (O-Oxe2x80x2) of the fan (6) at predetermined intervals in the direction of the radius of the fan (6). The plurality of board-shaped ribs (41, 41 . . . ) are extended in the direction of rotation of the fan (6) and also inclined in the direction of air flowing from the fan (6).
As stated before, there is a case where the air blowing unit is applied to the outer unit of an air-conditioning system. In this case, the occurrence of a short-circuit must be prevented as much as possible because it decreases the air-conditioning performance. The air taken in through the opening for air intake on the back side of the casing passes through a heat exchanger and then is blown off through the air outlet (2a) on the front side of the fan (6). It is necessary to avoid a phenomenon in which the blown air is again taken in through the opening for air intake and supplied to the heat exchanger. However, the current from the fan (6) arranged upstream of the fan guard (4) tends to flow outward in the direction of the radius of the fan (6). Consequently, if nothing is done, it is likely that the current from the fan guard (4) adheres to the surface of the front wall of the casing due to Coanda effect and travels towards the heat exchanger on the rear side, thereby causing a short circuit.
Therefore, in the second invention, the plurality of board-shaped ribs (41) are extended in the direction of rotation of the fan (6). As a result, the board-shaped ribs (41) make a force (Fr) inward in the direction of the radius of the fan (6) act on the current outward in the direction of the radius of the fan (6). Consequently, the current from the fan guard (4) is prevented from flowing outward in the direction of the radius of the fan (6), which reduces the occurrence of a short circuit as much as possible.
The second invention further comprises a plurality of nearly cylindrical ribs (42) which are integrated with the board-shaped ribs (41) and arranged concentrically. This structure makes the whole current in the direction of the radius of the fan (6) be converged forward due to the effect of the nearly cylindrical ribs (42) controlling the direction of the current. This prevents the occurrence of a short circuit further effectively.
As stated above, the current generated by the fan (6) and flowing into the fan guard (4) becomes spinning currents having a speed component in the direction of rotation of the fan (6). As a result, if the direction of the current generated by the fan (6) does not agree with the angle at which the board-shaped ribs (41) are installed, the current is split and noise occurs.
Therefore, in the second invention, the board-shaped ribs (41) are inclined in the direction of air flowing from the fan (6). As a result, the direction of the current from the fan (6) agrees with the angle at which the board-shaped ribs (41) are installed, which can reduce the splitting of the current as much as possible, thereby further lowering the noise.
Since the ribs (41) of the second invention are shaped like boards, the current generated by the fan (6) smoothly follows the surfaces of the board-shaped ribs (41). As a result, splitting of current occurs less, which eliminates the pressure loss and lowers the noise.
(3) Third Invention
The third invention is provided with a frame (4a) arranged around the perimeter of an air outlet (2a) of a fan (6), and further with a plurality of board-shaped ribs (41, 41 . . . ) extending radially from the vicinity of the center of the frame (4a) outward in the direction of the radius of the fan (6).
A line (A) connecting an air inlet end (41a) and an air outlet end (41b) of a board-shaped rib (41) in the cross section perpendicular to a line (C1) formed by the air outlet end (41b) of the board-shaped rib (41) is inclined from the rotation axis (O-Oxe2x80x2) by a predetermined angle (xcex8r) of installment in the direction of rotation of the fan (6).
In addition, a point (P2) on the outer circumference of the air outlet end (41b) of the board-shaped rib (41) is positioned at a point rotated the direction of rotation of the fan (6) from a straight line (B) connecting a point (P1) on the inner circumference of the air outlet end (41a) and the rotation axis (O-Oxe2x80x2).
In other words, the third invention comprises a frame (4a) arranged around the perimeter of the air outlet (2a) of the fan (6), and a plurality of board-shaped ribs (41, 41 . . . ) extending radially from the vicinity of the center of the frame (4a) corresponding to the rotation axis (O-Oxe2x80x2) of the fan (6) outward in the direction of the radius of the fan (6). In a cross section perpendicular to the line (C1) formed by projecting the air outlet end (41b) of each of the plurality of board-shaped ribs (41, 41 . . . ) on a surface perpendicular to the rotation axis (O-Oxe2x80x2) of the fan (6), a line (A) connecting a point (PL) on the air inlet end (41a) of each of the plurality of board-shaped ribs (41, 41) and a point (PT) on the air outlet end (41b) is inclined from the rotation axis (O-Oxe2x80x2) of the fan (6) by a predetermined angle (xcex8r) of installment in the direction of rotation of the fan (6). In addition, the point (P2) closest to the frame (4a) on the line (C1) formed by projecting the air outlet end (41b) of each of the plurality of board-shaped ribs (41, 41 . . . ) on a surface perpendicular to the rotation axis (O-Oxe2x80x2) of the fan (6) is positioned at a point rotated the direction of rotation of the fan (6) from the straight line (B) connecting a point of intersection (O) of the rotation axis (O-Oxe2x80x2) of the fan (6) and the projection surface and the point (P1) closest to the center portion.
As stated before, there is a case where the air blowing unit is applied to the outer unit of an air-conditioning system. In this case, the occurrence of a short-circuit must be prevented as much as possible because it decreases the air-conditioning performance. The air taken in through the opening for air intake on the back side of the casing passes through a heat exchanger and then is blown off through the air outlet (2a) on the front side of the fan (6). It is necessary to avoid a phenomenon in which the flown air is again taken in through the opening for air intake and supplied to the heat exchanger. However, the current generated by the fan (6) arranged upstream of the fan guard (4) tends to flow outward in the direction of the radius of the fan (6). Consequently, if nothing is done, it is likely that the current from the fan guard (4) adheres to the surface of the front wall of the casing due to Coanda effect and travels towards the heat exchanger on the rear side, thereby causing a short circuit.
Therefore, the third invention comprises the plurality of board-shaped ribs (41) extending radially outward in the direction of the radius of the fan (6). The board-shaped ribs (41) are so shaped that the line (A) connecting an air inlet end (41a) and an air outlet end (41b) is inclined from the rotation axis (O-Oxe2x80x2), and that the point (P2) on the outer circumference of the air outlet end (41b) is positioned at a point rotated in the direction of rotation of the fan (6) from the point (P1) on the inner circumference.
Employing ribs shaped like this makes a force (Fr) inward in the direction of the radius of the fan (6) due to the board-shaped ribs (41) act on the current generated by the fan (6). Consequently, the current from the fan guard (4) is prevented from flowing outward in the direction of the radius of the fan (6), which reduces the occurrence of a short circuit as much as possible.
Since the ribs (41) of the third invention are shaped like boards, the current generated by the fan (6) smoothly follows the surfaces of the board-shaped ribs (41). As a result, splitting of current occurs less, which eliminates the pressure loss and lowers the noise.
(4) Fourth Invention
The fourth invention is provided with a frame (4a) arranged around the perimeter of an air outlet (2a) of a fan (6), and further with a plurality of board-shaped ribs (41, 41 . . . ) extending radially from the vicinity of the center of the frame (4a) outward in the direction of the radius of the fan (6). The fourth invention is further provided with a plurality of nearly cylindrical ribs (42, 42 . . . ) which are integrated with the plurality of board-shaped ribs (41, 41 . . . ) and arranged concentrically around the rotation axis (O-Oxe2x80x2) of the fan (6) at predetermined intervals in the direction of the radius of the fan (6).
A line (A) connecting an air inlet end (41a) and an air outlet end (41b) of a board-shaped rib (41) in the cross section perpendicular to a line (C1) formed by the air outlet end (41b) of the board-shaped rib (41) is inclined from the rotation axis (O-Oxe2x80x2) by a predetermined angle (xcex8r) of installment in the direction of rotation of the fan (6).
In addition, a point (P2) on the outer circumference of the air outlet end (41b) of the board-shaped rib (41) is positioned at a point rotated in the direction of rotation of the fan (6) from a straight line (B) connecting a point (P1) on the inner circumference of the air outlet end (41a) and the rotation axis (O-Oxe2x80x2).
In other words, the fourth invention comprises a frame (4a) arranged around the perimeter of the air outlet (2a) of the fan (6), a plurality of board-shaped ribs (41, 41 . . . ) extending radially from the vicinity of the center of the frame (4a) corresponding to the rotation axis (O-Oxe2x80x2) of the fan (6) outward in the direction of the radius of the fan (6), and a plurality of nearly cylindrical ribs (42, 42 . . . ) which are integrated with the plurality of board-shaped ribs (41, 41 . . . ) and arranged concentrically around the rotation axis (O-Oxe2x80x2) of the fan (6) at predetermined intervals in the direction of the radius of the fan (6). In a cross section perpendicular to the line (C1) formed by projecting the air outlet end (41b) of each of the plurality of board-shaped ribs (41, 41 . . . ) on a surface perpendicular to the rotation axis (O-Oxe2x80x2) of the fan (6), a line (A) connecting a point (PL) on the air inlet end (41a) of each of the plurality of board-shaped ribs (41, 41) and a point (PT) on the air outlet end (41b) is inclined from the rotation axis (O-Oxe2x80x2) of the fan (6) by a predetermined angle (xcex8r) of installment in the direction of rotation of the fan (6). In addition, the point (P2) closest to the frame (4a) on the line (C1) formed by projecting the air outlet end (41b) of each of the plurality of board-shaped ribs (41, 41 . . . ) on a surface perpendicular to the rotation axis (O-Oxe2x80x2) of the fan (6) is positioned at a point rotated in the direction of rotation of the fan (6) from the straight line (B) connecting a point of intersection (O) of the rotation axis (O-Oxe2x80x2) of the fan (6) and the projection surface and the point (P1) closest to the center portion.
As stated before, there is a case where the air blowing unit is applied to the outer unit of an air-conditioning system. In this case, the occurrence of a short-circuit must be prevented as much as possible because it decreases the air-conditioning performance. The air taken in through the opening for air intake on the back side of the casing passes through a heat exchanger and then is blown off through the air outlet (2a) on the front side of the fan (6). It is necessary to avoid a phenomenon in which the blown air is again taken in through the opening for air intake and supplied to the heat exchanger. However, the current generated by the fan (6) arranged upstream of the-fan guard (4) tends to flow outward in the direction of the radius of the fan (6). Consequently, if nothing is done, it is likely that the current from the fan guard (4) adheres to the surface of the front wall of the casing due to Coanda effect and travels towards the heat exchanger on the rear side, thereby causing a short circuit.
Therefore, the fourth invention comprises the plurality of board-shaped ribs (41) extending radially outward in the direction of the radius of the fan (6). The board-shaped ribs (41) are so shaped that the line (A) connecting the air inlet end (41a) and the air outlet end (41b) is inclined from the rotation axis (O-Oxe2x80x2), and that the point (P2) on the outer circumference of the air outlet end (41b) is positioned at a point rotated in the direction of rotation of the fan (6) from the point (P1) on the inner circumference.
Employing the ribs shaped like this makes a force (Fr) inward in the direction of the radius of the fan (6) due to the board-shaped ribs (41) act on the current generated by the fan (6). Consequently, the current from the fan guard (4) is prevented from flowing outward in the direction of the radius of the fan (6), which reduces the occurrence of a short circuit as much as possible.
The fourth invention further comprises a plurality of nearly cylindrical ribs (42) which are integrated with the board-shaped ribs (41) and arranged concentrically. This structure makes the whole current in the direction of the radius of the fan (6) be converged forward due to the effect of the nearly cylindrical ribs (42) controlling the direction of the current. This prevents the occurrence of a short circuit further effectively.
As stated above, the current generated by the fan (6) and flowing into the fan guard (4) becomes spinning currents having a speed component in the direction of rotation of the fan (6). As a result, if the direction of the current generated by the fan (6) does not agree with the angle at which the board-shaped ribs (41) are installed, the current is split and noise occurs.
Therefore, in the fourth invention, the line (A) connecting the air inlet end (41a) and the air outlet end (41b) is inclined from the rotation axis (O-Oxe2x80x2) in the direction of rotation of the fan (6). As a result, the direction of the current from the fan (6) agrees with the angle at which the board-shaped ribs (41) are installed, which can reduce the splitting of the current as much as possible, thereby further lowering the noise.
Consequently, the plurality of board-shaped ribs (41) and the plurality of nearly cylindrical ribs (42) become approximately symmetrical with respect to the rotation axis (O-Oxe2x80x2). This structure can more effectively restrict a pressure loss resulting from a current collision due to the disagreement of the direction of the current from the fan (6) and the angle at which the ribs are installed, or noise resulting from the occurrence of vortexes.
Since the ribs (41) of the fourth invention are shaped like boards, the current generated by the fan (6) smoothly follows the surfaces of the board-shaped ribs (41). As a result, splitting of current occurs less, which eliminates the pressure loss and lowers the noise.
(5) Fifth Invention
According to the fifth invention, in any of the first to fourth inventions, the inner dimension ("psgr"1) of the frame (4a) is designed to be larger than the inner diameter ("psgr"2) of the edge of the air outlet (2a) upstream of the fan guard (4).
When the inner dimension ("psgr"1) of the frame (4a) is larger than the inner diameter ("psgr"2) of the edge of the air outlet (2a) upstream of the fan guard (4), it becomes possible to prevent the current generated by the fan (6) from causing interference with the frame (4a). This structure further improves the effect of reducing noise in any of the first to fourth inventions.
(6) Sixth Invention
According to the sixth invention, in any of the first to fourth inventions, the line (C1) formed by the air outlet end (41b) of each of the board-shaped ribs (41) is a curve where the angle (xcex8xcex1) which the line (C1) forms with the direction tangent to the nearly cylindrical ribs (42) grows from inside to outside in the direction of the radius of the fan (6).
In other words, according to the sixth invention, in any of the first to fourth inventions, the line (C1) formed by projecting the air outlet end (41b) of each of the plurality of board-shaped ribs (41, 41 . . . ) is a curve where the angles (xcex8xcex1, xcex8xcex1. . . ) which the line (C1) forms with the direction tangent to the plurality of nearly cylindrical ribs (42) grow from inside to outside in the direction of the radius of the fan (6).
This structure can prevent the force (Fr) (Refer to FIG. 6), which acts inwardly in the direction of the radius of the fan (6) from the board-shaped ribs (41), from becoming larger than necessary against the current from the fan (6), so as to increase the current resistance on the tip sides of the blades (6b, 6b . . . ) of the fan (6) which have a relatively large speed component in the axial direction.
(7) Seventh Invention
According to the seventh invention, in the sixth invention, the angle (xcex8r) at which the board-shaped ribs (41) are installed is designed to be approximately equal to the angle (xcex8i) at which air is generated by the fan (6) in the diametrical position (Rcmax) where the speed component (CZ) of the current from the fan (6) in the axial direction is the largest and is approximately uniform in the direction of the radius of the fan (6).
In other words, according to the seventh invention, in the sixth invention, the angle (xcex8r) at which the board-shaped ribs (41) are installed is designed to be approximately equal to the angle (xcex8i) of the current just generated by the blades of the fan (6) in the diametrical position (Rcmax) where the speed component (CZ) of the current from the blades of the fan (6) in the axial direction is the largest and is approximately uniform in the direction of the radius of the fan (6).
In the third, fourth, fifth, or sixth invention, the speed component of the current just generated by the fan (6) in the axial direction is lowered by a predetermined degree before it flows into the fan guard (4). On the other hand, due to law of conservation of angular momentum, the speed component of the current from the fan (6) in the circumferential direction is maintained at the opening of the fan guard (4). Consequently, the angle (xcex8n) between the axial direction and the direction tangent to the current flowing into the fan guard (4) is larger than the angle (xcex8i) of the current just generated by the fan (6).
In addition, the angle (xcex8i) of the current just generated by the fan (6) tends to increase as it gets closer to the hub (6a) than in the diametrical position (Rcmax) where speed component (CZ) of the current from the fan (6) in the axial direction is the largest. Consequently, it is pretty difficult to design the angle (xcex8r) of installment in a manner to make the angles (xcex8i) and (xcex8n) equal to each other.
Therefore, in the seventh invention, the angle (xcex8xcex1) between the line (C1) formed by the air outlet end (41b) of each of the board-shaped ribs (41) and the direction tangent to the nearly cylindrical ribs (42) is increased outward in the direction of the radius of the fan (6). Furthermore, the angle (xcex8r) at which the board-shaped ribs (41) are installed is designed to be approximately equal to the angle (xcex8i) of air flowing from the fan (6) in the position (Rcmax) where the speed component (CZ) of the current from the fan (6) in the axial direction is the largest.
As a result, the substantial angle (xcex8rs) of installing the ribs with respect to the current from the fan (6) can be designed to approximately agree with the angle (xcex8n) between the axial direction and the direction tangent to air flowing into the fan guard (4).
In that case, in the seventh invention, the angle (xcex8r) at which the board-shaped ribs (41) are installed is approximately uniform in the direction of the radius of the fan (6). Consequently, the above-mentioned substantial angle (xcex8rs) of installment becomes larger on the hub (6a) side than in the diametrical position (Rcmax) where the speed component (CZ) of the current from the fan (6) in the axial direction is largest, so that it agrees with air actually flowing into the fan guard (4).
Therefore, in the seventh invention, the effect of reducing noise can be obtained only by controlling the angle (xcex8i) of the current in the diametrical position (Rcmax) where the speed component (CZ) of the current from the fan (6) in the axial direction is largest. Thus, only controlling the angle (xcex8i) makes it possible that the substantial angle (xcex8rs) of installment in all positions in the direction of the radius of the fan (6) agrees with the air current, without complicated setting of the angle (xcex8r) at which the board-shaped ribs (41) are installed in the direction of the radius of the fan (6). As a result, the effect of reducing noise can be obtained by means of a simpler design.
(8) Eighth Invention
According to the eighth invention, in any of the first to fourth inventions, the number (Zr) of the board-shaped ribs (41) and the number (Zb) of the blades (6b) of the fan (6) are relatively prime, and when the midpoint position of the curve (C1) formed by the air outlet end (41b) of each of the board-shaped ribs (41) and the midpoint position of the curve (C2) formed by the rear edge of each of the blades (6b) of the fan (6) coincide with each other with respect to a surface perpendicular to the rotation axis (O-Oxe2x80x2), these curves (C1, C2) are designed to cross each other.
In other words, according to the eighth invention, in any of the first to seventh inventions, the number (Zr) of the board-shaped ribs (41) and the number (Zb) of the blades (6b) of the fan (6) are relatively prime, and when the curve (C2) formed by projecting the rear edge of each of the blades (6b, 6b . . . ) of the fan (6) is rotated in such a manner as to make the midpoint position of the curve (C2) agree with the midpoint position of the curve (C1) formed by projecting the air outlet end (41b) of each of the board-shaped ribs (41,41 . . . ) on a surface perpendicular to the rotation axis (O-Oxe2x80x2) of the fan (6), these curves (C1, C2) are designed to cross each other.
In general, the current just generated by the fan (6) having a speed component in the direction of rotation of the fan is influenced by a boundary layer or a split region developed on the negative pressure surface of the blades (6b). Consequently, there are main stream portions having a current with high velocity among the blades (6b) and rear stream portions having a current with low velocity in the vicinity of each blade (6b). When seen from the plurality of board-shaped ribs (41, 41 . . . ) side while they are in a stationary state, the main stream portions and the rear stream portions of different velocities pass through the air inlet ends alternately. As a result, the surfaces of the board-shaped ribs (41) have a pressure fluctuation whose main component is a frequency corresponding to the product of the number of revolutions N of the fan (6) and the number (Zb) of the blades (6b), which causes so-called NZ noise.
However, in the eighth invention, the number (Zr) of the plurality of board-shaped ribs (41, 41 . . . ) and the number (Zb) of the blades (6b, 6b . . . ) are made to be relatively prime, thereby making it possible to shift in time the interference between the rear streams of the blades (6b) and the plurality of board-shaped ribs (41, 41 . . . ) arranged in the direction of the perimeter. As a result, the NZ noises have different phases in the direction of the radius of the fan (6), which makes the NZ noises weaken each other, so as to reduce the occurrence of the NZ noises.
On the other hand, when the curve (C2) formed by projecting the rear edge of each of the blades (6b) of the fan (6) is rotated so as to coincide with the curve (C1) formed by projecting the air outlet end (41b) of each of the board-shaped ribs (41) on a surface perpendicular to the rotation axis (O-Oxe2x80x2) of the fan (6), the NZ noises increase remarkably. In this case, the rear streams of the current from the fan (6) pass through the board-shaped ribs (41) in the direction of the radius of the fan (6). This remarkably increases the NZ noises resulting from the interference between the rear streams from the blades (6b) and the board-shaped ribs (41).
Therefore, in the eighth invention, when the midpoint position of the curve (C1) of the air outlet end (41b) of each of the board-shaped ribs (41) agrees with the midpoint position of the curve (C2) of the rear edge of each of the blades (6b) of the fan (6) with respect to a surface perpendicular to the rotation axis (O-Oxe2x80x2) of the fan (6), these curves (C1, C2) are designed to cross each other. This structure can shift in time the interference between the rear streams of the blades (6b) and the plurality of board-shaped ribs (41). As a result, the NZ noises have different phases in the direction of the radius of the fan (6), which makes the NZ noises weaken each other, so as to reduce the occurrence of the NZ noises.
Thus, according to the eighth invention, the fan guard (4) can be further thinned, while maintaining the effects of reducing noise and preventing the occurrence of a short circuit in any of the first to seventh inventions.
(9) Ninth Invention
According to the ninth invention, in any of the first to eighth inventions, the air inlet ends (41a, 42a) of the board-shaped ribs (41) or the nearly cylindrical ribs (42) are designed to be approximately arc in cross section.
In general, the current generated by the fan (6) fluctuates over time, so that the angle at which air flows into the board-shaped ribs (41) or the nearly cylindrical ribs (42) of the fan guard (4) also fluctuates over time.
Therefore, in the ninth invention, the ribs (41, 42) are designed to be approximately arc in cross section so that the pressure fluctuation on the rib surfaces can be reduced effectively even if the angle of air flowing into the board-shaped ribs (41) or the nearly cylindrical ribs (42) fluctuates.
Consequently, the structure of the ninth invention further improves the effect of reducing noise in any of the first to eighth inventions.
Furthermore, the angle of air flowing into the board-shaped ribs (41) or the nearly cylindrical ribs (42) of the fan guard (4) fluctuates greatly over time as it gets closer to the rear edges of the blades (6b) of the fan (6). Thus, in the present invention, the fan guard (4) can be designed to be thinner.
(10) Tenth Invention
According to the tenth invention, in any of the first to ninth inventions, the thickness (T2) of the air outlet ends (41b, 42b) of the board-shaped ribs (41) or the nearly cylindrical ribs (42) is designed to be smaller than the maximum thickness (T1).
Thus forming the cross sectional profiles of the board-shaped ribs (41) or the nearly cylindrical ribs (42) facilitates the mixing of current on the surfaces of the ribs (41, 42) which occurs immediately after the board-shaped ribs (41) or the nearly cylindrical ribs (42), thereby making it harder to develop vortexes behind the ribs (41, 42). As a result, the effects in any of the first to ninth inventions can be fully exerted even when it is necessary to increase the thickness of the ribs (41, 42) in order to provide enough strength.
(11) Eleventh Invention
According to the eleventh invention, in any of the first to tenth inventions, a sealing plate (43) is provided at the center of the frame (4a) corresponding to the rotation axis (O-Oxe2x80x2) of the fan (6).
In general, in the distribution of current in the direction of the radius of the fan (6) inside the hub (6a), there is a reverse current which goes from the downstream side of the fan (6) towards the hub (6a) side. The reverse current interferes with the current flowing in the intended direction, thereby causing an issue of noise.
In the eleventh invention, a sealing plate (43) is provided at the center of the fan guard (4) and is made to correspond to the rotation axis (O-Oxe2x80x2) of the fan (6). The sealing plate (43) covering the center of the fan guard (4) restricts the interference between the current flowing towards the air outlet and the reverse current, thereby further reducing the noises.
(12) Twelfth Invention
According to the twelfth invention, in any of the first to eleventh invention, the frame (4a) is designed to be approximately rectangular.
The current from the fan (6) varies in velocity among different positions in the direction of the radius of the fan (6). As stated above, the air flowing from the outer portions of the blades of the fan (6) that are a little closer to the hub (6a) than the tips of the blades has a higher velocity than the current from the tips. The velocity of the current decreases from these portions both towards the hub (6a) and towards the tips. The current shows such a velocity distribution in the direction of the radius of the fan (6).
In the twelfth invention, the frame (4a) of the fan guard (4) is approximately rectangular, and the current from the fan (6) is led to four corners. Above all, the velocity of flow of air from the outer portions of the blades (6b) of the fan (6) that are a little closer to the hub (6a) than the tips of the blades can be decreased effectively within a short distance.
The twelfth invention has a feature of increasing the effective area of the fan guard (4) when the casing of the air blowing unit is shaped like a rectangular box, thereby efficiently improving the effects of the fifth invention.
In this case, the fan guard (4) is usually installed in the downstream part of the circular air outlet (2a) arranged on one surface of the rectangular casing. Since the fan guard (4) is approximately rectangular, there is an advantage that the casing can be used without changing the outer dimensions.
(13) Thirteenth Invention
According to the thirteenth invention, in any of the first to twelfth inventions, the air inlet ends (42a) of the nearly cylindrical ribs (42) are more protruded than the air inlet ends (41a) of the board-shaped ribs (41).
When the blades (6b) of the fan (6) pass through the positions of the board-shaped ribs (41), it is inevitable that some vortexes occur on each surface of the board-shaped ribs (41). On the other hand, the nearly cylindrical ribs (42), which are along the current from the fan (6), cause almost no vortexes.
However, when the air inlet ends (41a) of the board-shaped ribs (41) are more protruded than the air inlet ends (42a) of the nearly cylindrical ribs (42), vortexes occur at the air inlet ends (42a) of the nearly cylindrical ribs (42) in the portions where the board-shaped ribs (41) and the nearly cylindrical ribs (42) cross each other.
Therefore, in the present invention, the air inlet ends (42a) of the nearly cylindrical ribs (42) are more protruded than the air inlet ends (41a) of the board-shaped ribs (41) so as to prevent the occurrence of vortexes at the air inlet ends (42a) of the nearly cylindrical ribs (42). Consequently, noises caused by the occurrence of the vortexes can be prevented.
(14) Fourteenth Invention
According to the fourteenth invention, in any of the first to thirteenth inventions, the air inlet ends (42a) of the nearly cylindrical ribs (42) are more protruded than the air inlet ends (41a) of the board-shaped ribs (41), and the air outlet ends (42b) of the nearly cylindrical ribs (42) are more protruded than the air outlet ends (41b) of the board-shaped ribs (41).
The fan guard is usually molded by pulling out two molds in the direction of the air inlet ends (41a, 42a) and the air outlet ends (41b, 42b) of the board-shaped ribs (41) and the nearly cylindrical ribs (42).
In this case, if the air inlet ends (41a) and the air outlet ends (41b) of the board-shaped ribs (41) were more protruded than the air inlet ends (42a) and the air outlet ends (42b) of the nearly cylindrical ribs (41), undercut or other problems would occur at the portions where the board-shaped ribs (41) and the nearly cylindrical ribs (42) cross each other. As a result, it would take time to mold the fan guard (4).
Therefore, in the present invention, the molding is facilitated by making the air inlet ends (42a) and the air outlet ends (42b) of the nearly cylindrical ribs (42) be more protruded than the air inlet ends (41a) and the air outlet ends (41b) of the board-shaped ribs (41).
(15) Fifteenth Invention
The fifteenth invention relates to an air-conditioning device provided with the fan guard (4) of the air blowing unit of any of the first to fourteenth inventions. The air-conditioning device is provided with a heat source side unit (50) and a user""s side unit, and the heat source side unit (50) includes at least a heat exchanger and a fan stored in a casing (51). The casing (51) is provided with an air outlet (54), which is covered by the fan guard (4).
The fifteenth invention is an air-conditioning device which can exert the effects of any of the first to fourteenth inventions. The air-conditioning device of the present invention prevents the occurrence of a short circuit effectively, which secures prevention of a decrease in air conditioning performance.
The provision of the nearly cylindrical ribs (42) makes the whole current in the direction of the radius of the fan (6) be converged forward due to the effect of the nearly cylindrical ribs (42) controlling the direction of the current. This prevents the occurrence of a short circuit further effectively.
The splitting of the current at the fan guard (4) occurs less, which eliminates the pressure loss and lowers the noise.
The NZ noises in the fan guard (4) have different phases in the direction of the radius of the fan (6), which makes the NZ noises weaken each other, so as to reduce the occurrence of the NZ noises.
Making the air inlet ends (41a, 42a) of the board-shaped ribs (41) or the nearly cylindrical ribs (42) approximately arc in cross section, the fan guard (4) can be designed further thinner.
Providing the sealing plate (43) at the center of the fan guard (4) restricts the interference between air flowing towards the air outlet and the reverse current, thereby further reducing the noises.
In the case where the casing (51) is shaped like a rectangular box, designing the frame (4a) to be approximately rectangular can increase the effective area of the fan guard (4).